/*    $OpenBSD: arc4.c,v 1.3 2007/09/11 12:07:05 djm Exp $    */
/*
 * Copyright (c) 2003 Markus Friedl <markus@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>

#include <crypto/arc4.h>

#define RC4SWAP(x,y) \
do { \
u_int8_t t = ctx->state[x];  \
ctx->state[x] = ctx->state[y]; \
ctx->state[y] = t; \
} while(0)

void
rc4_keysetup(struct rc4_ctx *ctx, u_char *key, u_int32_t klen)
{
    u_int8_t x, y;
    u_int32_t i;
    
    x = y = 0;
    for (i = 0; i < RC4STATE; i++)
        ctx->state[i] = i;
    for (i = 0; i < RC4STATE; i++) {
        y = (key[x] + ctx->state[i] + y) & (RC4STATE - 1);
        RC4SWAP(i, y);
        x = (x + 1) % klen;
    }
    ctx->x = ctx->y = 0;
}

void
rc4_crypt(struct rc4_ctx *ctx, u_char *src, u_char *dst,
          u_int32_t len)
{
    u_int32_t i;
    
    for (i = 0; i < len; i++) {
        ctx->x = (ctx->x + 1) & (RC4STATE - 1);
        ctx->y = (ctx->state[ctx->x] + ctx->y) & (RC4STATE - 1);
        RC4SWAP(ctx->x, ctx->y);
        dst[i] = src[i] ^ ctx->state[
                                     (ctx->state[ctx->x] + ctx->state[ctx->y]) & (RC4STATE - 1)];
    }
}

void
rc4_getbytes(struct rc4_ctx *ctx, u_char *dst, u_int32_t len)
{
    u_int32_t i;
    
    for (i = 0; i < len; i++) {
        ctx->x = (ctx->x + 1) & (RC4STATE - 1);
        ctx->y = (ctx->state[ctx->x] + ctx->y) & (RC4STATE - 1);
        RC4SWAP(ctx->x, ctx->y);
        dst[i] = ctx->state[
                            (ctx->state[ctx->x] + ctx->state[ctx->y]) & (RC4STATE - 1)];
    }
}

void
rc4_skip(struct rc4_ctx *ctx, u_int32_t len)
{
    for (; len > 0; len--) {
        ctx->x = (ctx->x + 1) & (RC4STATE - 1);
        ctx->y = (ctx->state[ctx->x] + ctx->y) & (RC4STATE - 1);
        RC4SWAP(ctx->x, ctx->y);
    }
}
